In recent years recombinant DNA technology has been used to circumvent many limitations of traditional plant breeding programs. This technology has allowed workers to (i) identify and clone desirable genes (such as, genes expressing products that confer disease and insect resistance (Herreraestrella, et al., 1995), (ii) transfer such genes into plants (Walkerpeach, et al., 1994), and (iii) alter selected plant phenotypes by the expression of such genes (Ferro, et al., 1995; Benfey, et al., 1990; Klee, et al., 1991).
A large number of examples of plant promoters useful for the expression of selected genes in plants are now available (Zhu, et al., 1995; Ni, et al., 1995). These promoters have been used to drive the expression of foreign (or heterologous) genes in plants. In most cases, the 5' non-coding regions of the genes (i.e., regions immediately 5' to the coding region) have been used to generate chimeric genes. These regions are often referred to as promoter or transcriptional regulatory sequences. Promoters useful for the expression of a selected nucleic acid sequence in plants can be derived from plant DNA or from other sources, for example, plant viruses. In most cases, it has been demonstrated that sequences up to about 500-1500 bases allow regulated expression of genes under their control.
Expression of heterologous genes or selected sequences of genes in transgenic plants has typically involved the use of constitutive promoters. Exemplary plant promoters include the following: 35S Cauliflower Mosaic Virus (CaMV 35S), mannopine synthase, and octopine synthase (ocs). Such promoters have been used successfully to direct the expression of heterologous nucleic acid sequences in transformed plant tissue. However, when used to express DNA sequences in transgenic plants these promoters typically provide low level, constitutive expression (i.e., expression in all plant tissue).
Other promoters have been identified that allow tissue specific expression, for example, fruit specific expression, such as the E4 and E8 promoters from tomatoes (Cordes, et al., 1989; Bestwick, et al., 1995). Also, it has been demonstrated that nucleic acid sequences placed under the regulatory control of the 5' non-coding region of the tomato 2AII gene (Van Haaren) are preferentially transcribed in developing fruit tissue. Fruit specific regulation of the kiwifruit actinidin promoter has been reported to be conserved in transgenic petunia plants (Lin, et al., 1993).